1. Field of the Invention
The present invention relates to an apparatus for drying flat articles, and more particularly, to a drying apparatus which utilizes a vacuum-generating device for enhancing the speed of the drying operation.
2. Description of the Prior Art
In a first category of known drying apparatus of the kind mentioned, the surface serving to support the flat articles to be dried is a heated plane surface, oriented to be in a horizontal or inclined position, and of relatively limited dimensions, so that the operators can lay thereon the articles to be dried. However, the minimum economically acceptable dimensions do not allow the operators to lay out readily all portions of the articles or pieces to be dried, so that some portions often cannot be handled as well as is required to produce good work, thus resulting in a loss in the useful area of the articles and in a substantial economic loss. Moreover, the limited dimensions of the plane support surface do not enable the drying of articles of large dimensions which must therefore be divided, thus becoming unsuitable for certain uses and of consequently reduced value.
Furthermore, the production provided with the aid of a single heated support surface is relatively small. A moderate industrial production necessitates a plurality of these apparatus. In the case of known plane support surfaces, this multiplication of the individual apparatus or a group of such apparatus is costly and the apparatus occupy a substantial space.
In another category of known apparatus, the flat articles to be dried are deposited on a heated cylindrical support surface partially surrounded by an endless flexible band rotating intermittently. Complete drying cannot be effected in practice in such apparatus because:
(a) if the flexible endless band is fluid-tight, it cannot allow any evaporation of liquid contained in the articles to be dried;
(b) if the flexible endless band is porous, it will allow a very slow evaporation of the liquid, but experience has shown that articles to be dried containing generally 60-100% by weight of liquid in relation to the dry material require a drying duration of about 30 minutes at a temperature of about 90.degree. C. which is not acceptable for good quality products. A temperature lower than 50.degree. C., as necessary to preserve the quality of the products, requires a drying duration of from one to three hours.
The resultant production of an apparatus of this kind is thus reduced to only several articles per day, which shows that this idea does not give rise to effective utilization. In fact, apparatus of this kind are used only for ironing or finishing of the articles and not for drying.
The present invention has primarily as its object to provide an apparatus for drying under vacuum flat articles or pieces of porous material, which avoids the disadvantages referred to hereinbefore and facilitates the work of the operators by allowing them to operate continuously at the same place, situated at a convenient height, and at a suitable small distance in front of them. Another object of the invention is to provide an apparatus of the noted kind which is of relatively compact construction and does not require substantial manipulating space in order to open and to close the one or more cover means.